It is so widely recognized as to be a truism that repeatedly using muscular effort will forestall the loss of or restore muscular strength. Physical therapy is partly based on this truism. Thus, physically challenged patients are encouraged to exercise the portions of their muscle structure which have become incapacitated through injury or stroke.
In the case of invalids having limited strength or control in their lower limbs, the use of rocking chairs has been found of benefit. If resistance is added to the rocking of a rocking chair, it stands to reason that the victim will benefit even further.